I didn't know about the pressure adjustment until Martin told me. There are pumps on the market with some kind of pressure sensor that adjust the pressure gradually, making for a smoother delivery and eliminating water hammer. I haven't looked into them.
Yea, the 8 gallons of water.... that is really disappointing. I haven't gotten my water system working. Too busy at work, family obligations etc...
About the water bladder; I found the Plastimo 13gal "flexible tank" on line. The specs are 27.3" x 27.3 x 9". I am assuming that when there is no water in it that the 27.3" is the full outside width. Usually anything like that is the full outside measurements (kb7our, if you have the tank out, lay it flat and measure it for us please.) Then just inside that is the weld that holds the top and bottom together, leaving about 26.5 inside that expand to hold water. I measured the space in the front AT cabinet "foot well" where the tank lays. I measured the circumference side to side and front to back. Side to side measures 58.75" and front to back is 61.75. The material in the Plastimo tank that can expand is 26.5 x 2 or 53". So it can never fill the space in the foot well. The next bigger tank Plastimo has is the same one but longer, so one of the dimensions is still not going to be filled. When you add the corners that come up short on two dimensions there could be 3 to 5 gallons of space not filled. That's why I bought a different one. I found one that is 36" x 36".
My plan is to measure the water I pour into it to fill it up and then pump it dry to see how much is usable. Report later.
I'm have installer's block. I can't figure out exactly how I want it installed and I can't get motivated to finish it...